Alerting device having oscillations of negative resistance circuit controlled by mechanical resonance of transducer



May 27, 1969 POTTER A 3,447,151

ALERTING DEVICE HAVING OSCILLATIONS OF NEGATIVE RESISTANCE CIRCUIT CONTROLLED BY MECHANICAL RESONANCE 0F TRANSDUCER Filed March 25, 1967 "LT i 33 '2 FIGI Iii FIG 2 FIG 4 United States Patent ALERTING DEVICE HAVING OSCILLATIONS OF NEGATIVE RESISTANCE CIRCUIT CON- TROLLED BY MECHANICAL RESONANCE OF TRANSDUCER Bronson M. Potter, RED. 1, Greenville, N.H. 03048 Continuation-impart of application Ser. No. 340,392, Jan. 27, 1964. This application Mar. 23, 1967, Ser. No. 625,461

Int. Cl. G08b 3/00, 3/10 US. Cl. 340-384 13 Claims ABSTRACT OF THE DISCLOSURE This is a continuation-in-part of my application Ser. No. 340,392 filed Jan. 27, 1964, now abandoned.

Conventional alerting devices, such as bells, buzzers, and the like typically used in telephones, alarm mechanisms, and other signal systems, are heavy, expensive, and quite large. Further, they are inefficient in their production of sound or light output in comparison with their electrical power input. Although desirable, it has not been possible to employ alerting devices in many circuit designs because of their current and voltage requirements or their unreliability.

It is therefore an object of this invention to provide a simple, small, lightweight, reliable alerting device which is highly efiicient to operate, has a minimum of moving parts and is very inexpensive to manufacture.

The alerting device featured by this invention includes a transducer that has a vibratory surface from which acoustic energy is radiated. This transducer has a predetermined resonant frequency, and when vibrating at that frequency can radiate substantial acoustic energy substantially within the frequency range of the ears maximum sensitivity. The drive means for the vibratory surface may be powered through a circuit having :an active device which exhibits negative resistance characteristics i.e., having a region in which the current and voltage bear the relation that one decreases when the other increases. The active device and transducer are so related that the electrical manifestations of the resonant motion of the transducer causes transition of the active device through its negative resistance region to occur at a frequency which bears an integral ratio to the resonant frequency of the transducer. The invention also features a gas tube as an active device, which the transducer controls, and which in turn powers the transducer. In all cases the circuit and the transducer are so related that the impedance of the transducer is substantially matched to the circuit. In devices thus constructed the transducer can regulate the frequency of its own power source, and can overcome any defects in frequency matching during manufacture, or variations in its own resonant frequency as may occur with changes in barometric pressure, etc.; all of this leading to very simple, reliable, effective and exceedingly inexpensive alerting devices.

Preferred embodiments of the invention feature the use of a simple two terminal :active device, and the circuit acts as a relaxation oscillator.

Preferred embodiments of the invention feature an active device in the circuit capable of emitting a light signal; a current-unique negative resistance active device for the relaxation oscillator; a small whole integer ratio between the frequency of the circuit and the resonant frequency of the transducer, preferably the ratio being unity and the resonant frequency being between 1 and 5 kilocycles; and electrical characteristics of the circuit so limited as to adapt the device to telephone line functions.

Other objects, features, and advantages will appear from the following description of preferred embodiments of the invention, taken together with the attached drawings thereof, in which:

FIG. 1 is a schematic of a circuit in accordance with this invention.

FIG. la is a schematic of a circuit similar to 'FIG. 1 employing a gas tube as a negative resistance element.

FIG. 2 is a schematic of another circuit in accordance with this invention using a gas tube as a negative resistance element.

FIG. 3 is a schematic of another circuit in accordance with this invention using an electromagnetic transducer and gas tube.

FIG. 4 is a schematic of a circuit similar to FIG. 3 using a four-layer semiconductor as the negative resistance element.

FIG. 5 is a schematic of another circuit in accordance with this invention using an avalanche diode.

FIG. 6 is a schematic of another circuit in accordance with this invention employing an avalanche diode.

FIG. 7 is :a graphical representation of the currentvoltage characteristic of one typical negative resistance device.

There is shown in FIG. 1 a circuit having .a negative resistance or gas tube active element 12 in series with a load resistor 14 between terminals 16 and 18. A capacitor 20, and a transducer 31 are connected in parallel with the resistor. The transducer 31 has a characteristic frequency of resonance such that when vibrating at that frequency its vibrating surface radiates substantial audible energy. (With the present state of technology it is found that piezo crystal transducers are the best suited.)

With appropriate impedance matching it is found that the transducer can influence the frequency of activation of device 12, and when so activated the device 12 is capable of energizing the transducer to produce an effective audible warning or alerting signal with the expenditure of very little energy.

Generally speaking, the negative resistance device employed as element 12 may be either current unique or voltage unique or, in the sense that it exhibits hysteresis, a non-unique element. For the example of FIG. 1, 'a voltage-unique element 12 may be assumed to be employed.

Refer-ring to FIGS. 1 and 7, with the device 12 voltageunique, the voltage which appears across the device 12 is the algebraic sum of the voltage appearing across terminals 16 and 18 and the volt-age appearing across the parallel combination of the transducer 31, the capacitor 20 and the resistor 14.

A part of the voltage appearing across the combination of the three elements is due to the resonant motion of the transducer which in this case is conventionally through of as generating a back EMF. This portion of the voltage influences the timing of the excursions through the negative resistance regions of the device 12, to cause the oscillations to synchronize With the transducer.

Advantageously, the transducer 31 controls the oscillations of the circuit at a frequency bearing an integral relation to the frequency of the transducer, and the thus controlled circuit can power the transducer driving memher in a highly efficient manner. The vibrating surface of the transducer, which may be a separate diaphragm, or an integral part of the driving member, vibrates with the driving member to produce audible sound energy at the frequency of oscillation of the circuit and crystal, or some harmonic thereof. Because the transducer can vibrate at or near its natural frequency, maximum output can be obtained with a minimum of input power.

The embodiment of FIG. 1a employs a gas tube 22 as the active device and a transducer 34 having a piezoelectric crystal as the drive means.

In operation, FIG. 1a, a voltage is applied to terminals 16 and 18 through a current-limiting resistor 14. The open circuit voltage of the voltage source is appreciably in excess of that value required to ignite gas tube 22. Therefore at the beginning of the cycle the tube is ignited, current flows through it, and the voltage appearing between terminals 28 and 18 rises from zero. This increase in voltage reduces the current through the tube 22 until a point is reached when the tube ceases to conduct. With the tube not conducting the resistor 14 discharges those elements in parallel with it until the voltage between terminals 16 and 28 again exceeds ignition potential.

For synchronous operation the back EMF of the transducer, by its effect upon the terminal voltage at the tube, governs the timing of either ignition, deconization or both of the gas tube, thereby synchronizing the oscillation of the circuit directly to the resonant frequency of the transducer or to an integral ratio or submultiple thereof.

Thus, the gas tube may be considered as producing in the circuit simple rising and falling roughly exponential wave forms appearing across combination 14, and 34. The transducer superimposes upon these wave forms an oscillatory component as a result of back EMF of the transducer, which, with appropriate choice of elements 20 and 14, causes the gas tube 22 to fire at an integral ratio of the resonant frequency of the transducer or an integral submultiple thereof.

Particular values of 14 and 20 depend upon the detailed nature of the gas tube and the transducer, and also upon what integral ratio is desired, for a rougher tone choose a larger submultiple to increase the disparity.

In addition to the sound of the transducer, a warning light can be obtained directly from the firing gas tube or other device being employed. Referring to FIG. la this is achieved by window 31 provided in housing 33, through which the light generated by the gas tube 22 can be seen by the person to be alerted.

Since transducer 34 presents significant capacitive impedance, capacitor 20 may be removed from the circuit of FIG. 1a resulting in the circuit 36 of FIG. 2.

Transducer 34 may also be replaced by an electromagnetic transducer 38 and may be connected in series with capacitor 20 in parallel with tube 22 to form circuit 40, FIG. 3. Initially a voltage applied across terminal 16 and 18 in FIG. 3 appears across resistor 14. But as capacitor 20 charges, an ever larger portion of that voltage appears across electrodes 26 and 28 of tube 22 until the firing voltage of the tube is reached. When the tube conducts, capacitor 20 discharges through electro-magnetic device 38, producing an audible output from the device and cutting off tube 22.

A semiconductor having negative resistance charac teristics, such as a four-layer device, may be used in place of tube 22. Substituting such a device 42 in place of tube 22 in circuit 40 results in a circuit 47 of FIG. 4. In addition to four-layer devices, tunnel diodes, uni-junction transistors, avalanche switching diffused silicon trigger devices, and integrated circuits performing the same functions may be used as the active element in the alterting devices disclosed herein.

The invention features alerting devices in which the negative resistance device is current unique and has a break-over current less than 500 microamps and a breakback voltage greater than 2 volts. The circuit incorporates the negative resistance element in the form of a relaxation oscillator. The transducer used has an impedance substantially matched to that of the oscillator, a sharp resonant frequency between about 1 and 5 kilocycles, and substantial back EMF. The back EMF is adapted to trigger the negative resistance device over a substantial voltage range of the power source, thereby substantially locking the frequency of firing of the negative resistance such that said firing frequency and said resonant frequency have the relationship that one of said frequencies bears the ratio of a small Whole integer to the other.

Preferred embodiments of the invention feature alerting devices which are useful where a constant voltage is continually applied to a circuit, e.g. a telephone dial current, and a second voltage is imposed on the constant voltage to trigger the circuit, e.g. for ringing a telephone. A device suited for use in telephone monitoring and alerting circuits has been achieved in circuit 39 of FIG. 5. Circuit 39 consists of a pair of terminals 41, 43, a simple rectifying silicon diode 46, capacitors 44 and 48, resistors 50 and 52, an avalanche breakdown device 54, and transducer 34. The breakdown device may have a breakdown voltage of approximately 65 volts and may be a pair of diffused silicon trigger devices, in series, such as model TI42 produced by Texas Instruments Company.

For a realization of this circuit, the rectifying silicon diode 46 should be capable of withstanding the alternate inverse peaks on the telephone line plus the charged voltage of capacitor 44 plus any voltage spikes that may appear on the line. Thus the diode should have a PIV of 600 volts or more. The resistor 50 may be wirewound, of a capacity of at least 1 watt and resistance of 5000 ohms. The resistor 52 may have a resistance of 620 ohms. The capacitors 44 and 48 can be paper or electrolytic with a rating of 50 microfarads at volts D.C. With suitable components the circuit and transducer can be very small, easily fitted within the handset of a telephone.

In operation 50 volts D.C. can be applied to terminals 41 and 43 energizing a circuit through capacitor 44 and through the parallel path of resistor 50 and capacitor 48. Capacitor 44 charges to the full voltage applied save for the negligible loss through internal resistance of diode 46. Conduction ceases when both capacitors 44 and 48 are fully charged. When ringing is desired an AC. voltage of approximately 50 volts is superimposed on terminals 41, 43. The increased voltage is reflected by an increase in the charge on the capacitors. When the voltage on capacitor 48 reaches the breakdown voltage of device 54, the device triggers, permitting current to flow through resistor 52 and transducer 34. The negative resistance device 54 cuts off rapidly allowing the capacitive charge accumulated on transducer 34 to dissipate across resistor 52. The cycle repeats during the positive portion of the AC. voltage, and transducer 34, discharging and charging at its own rate, vibrates at its natural frequency producing audible sound energy with a high efficiency.

Referring now to FIG. 6, this embodiment comprises a pair of terminals 58, 60, a resistor 62, a four-layer di ode avalanche breakdown device 54, and transducer 34. A capacitor 64, shown in phantom, may be added to sharpen the response of the circuit.

For one realization, the four-layer diode may be Motorola M 4L 2052, the resistor 62 may be 3500 ohms, 1 watt, of carbon composition, and the capacitor 20 may be a 0.5 mfd., VDC, tolerance capacitor of any of the various types of ceramic, paper, plastic or deposited filrn. The transducer may be a piezoelectric crystal with integral diaphragm such as produced by Electropac Inc.

In adopting the principles stated above, the skilled person will of course select a transducer to have a sufiiciently high degree of electro-mechanical efficiency so that the electrical manifestation at the terminals of the transducer of the resonant motion of the transducer will generate a sufficient back voltage or a back current to synchronize or control the frequency of the particular circuit being employed.

It will be understood that, for the purposes of the present invention the skilled person will select his componentry, e.g. the capacitors, resistors and active devices for compatible operation with the transducer according to the foregoing principles. Standard texts on circuit design may be referred to for this purpose. Some of the factors to be observed are, for the transducer, its impedance level, nature of impedance, and voltage requirements; for the active negative resistance device, the character of its uniqueness, e.g. current or voltage, its sensitivity in regard to the magnitude of the signals required to effect its excursions; and generally the voltages available and the quality of the capacitors available. The invention in one respect lies in the realization that conventional, presently available and extremely inexpensive components mentioned herein can achieve the results described. In another aspect, however, the invention presents a broader principle which will be applicable to other componentry as it is developed. Thus, for the transducer, when a drive means is referred to broadly herein, it is intended to comprehend, in addition to piezo crystals, electrostatic, electrodynamic, moving armature and other types of electroacoustic or other acoustic transducers. It is equally contemplated, With improvement of materials that oscillators operating in the harmonic mode, as well as the relaxation mode can be employed. And as mentioned it is contemplated that gas tubes and current unique, voltage unique, and non-unique (because of hysteresis) active negative resistance devices can be employed.

What is claimed is:

1. An alerting device comprising a transducer having a vibratory surface from which acoustic energy is radiated and means to drive said surface, said transducer having at least one predetermined frequency of resonance and operable, when vibrating substantially at said frequency, to radiate substantial audible energy substantially within the frequency range of the ears maximum sensitivity, a circuit adapted to be connected to a power source, for energizing said drive means, said circuit including an active device having a region of apparent negative resistance in which the magnitudes of the current and terminal voltage bear the relationship that one decreases with increase of the other, said circuit and transducer constructed and arranged so that the electrical manifestation of the resonant motion of the transducer causes the transitions of said active device through said region of apparent negative resistance to occur at a frequency bearing an integral ratio to the resonant frequency of the transducer, thereby providing a synchronized oscillating power supply to said transducer, said circuit and transducer so related that the impedance of the transducer is substantially matched to the circuit, whereby an audible warning can be simply generated using a small amount of power.

2. The alerting device of claim 1 wherein said active device has only two terminals.

3. The alerting device of claim 1 wherein the circuit formed with said active device comprises a relaxation oscillator, said active device having stable states on opposite sides of said region of negative resistance and adapted to change states and thereby introduce energy into the circuit in said synchronization with said transducer.

4. The altering device of claim 1 wherein said integral ratio of the frequency of oscillation of the circuit to the resonant frequency of the transducer is unity, and the resonant frequency of said transducer lies within said frequency range of the ears maximum sensitivity.

5. The altering device of claim 1 wherein an active device in said circuit is adapted to emit light upon energization of said circuit to generate a signal light simultaneously with the provision of power to said transducer.

6. The alerting device of claim 5 wherein said active device which emits said light is a negative resistance device adapted substantially to provide power to said transducer.

7. The alerting device of claim 1 wherein said trans ducer comprises a piezo crystal adapted to directly transmit mechanical energy to said vibratory surface.

8. The alerting device of claim 1 wherein said negative resistance device is current-unique having a breakover current less than 500 microamps and a break-back voltage greater than 2 volts, the circuit which incorporates said negative resistance device comprising a relaxation oscillator, said transducer having an impedance substantially matched to that of said oscillator and having a sharp resonant frequency between about '1 and 5 kilocycles and substantial back EMF, said back EMF of said transducer adapted over a substantial voltage range of the power source to trigger said negative resistance device and thereby substantially lock its frequency of firing, such that the firing frequency and said resonant frequency have the relationship that one of said frequencies bears the ratio of a small whole integer to the other.

9. The alerting device of claim 8 for use in place of a bell on a telephone line, said circuit adapted so that the break-over current of said circuit can occur only with the application of a substantial voltage on said power source, whereby a bias voltage, less than said substantial voltage, may be maintatined on said circuit without energizing said alerting device while rendering the telephone exchange aware of non-use of the telephone line.

10. The alerting device of claim 8 wherein said active device is a solid state multilayer semiconductor device having avalanche diode characteristics.

11. An alerting device comprising a transducer having a vibratory surface from which acoustic energy is radiated and means to drive said surface, said transducer having at least one predetermined frequency of resonance and operable, when vibrating substantially at said frequency, to radiate substantial audible energy substantially within the frequency range of the ears maximum sensitivity, a circuit adapted to be connected to a power source, for energizing said drive means, said circuit including an active device having a region of apparent negative resistance in which the magnitudes of the current and terminal voltage bear the relationship that one decreases with increase of the other, said active device having only two terminals connected in the circuit, at least one of said terminals adapted both to transmit power between said transducer and said active device and to apply the electrical manifestations of the resonant motion of said transducer to said active device, said circuit and transducer constructed and arranged so that the electrical manifestation of the resonant motion of the transducer causes the transitions of said active device through said region of apparent negative resistance to occur at a frequency bearing an integral ratio to the resonant frequency of the transducer, thereby providing a synchronized oscillating power supply to said transducer, said circuit and transducer so related that the impedance of the transducer is substantially matched to the circuit, whereby an audible Warning can be simply generated using a small amount of power.

7 8 12. The alerting device of claim 11 wherein there is 1,821,698 9/1931 Fisher 331-126 X only a single active device in said circuit. 3,144,618 8/ 1964 Jones et a1 331-115 X 13. The alerting device of claim 11 wherein said trans- 3,237,123 2/1966 Watters 331-115 X ducer comprises a piczo crystal adapted to directly transmit mechanical energy to said vibratory surface. 5 FOREIGN PATENTS 145,963 5/1936 Austria. References Cited UNITED STATES PATENTS JOHN W. CALDWELL, Przmary Examiner.

2 031 7 2 193 Pipkin et 1 HAROLD I. PITTS, Assistant Examiner.

3,246,311 4/1966 Sack. 10 3,324,725 6/1967 Yerman. 3,341,841 9/1967 Stampfli 34o -3s4 307-885; 331-115 Disclaimer 3,447,151.Br0ns0n Zlf. Potter, Greenville NH. ALERTING DEVICE HAV- ING OSCILLATIONS OF NEGATIVE RESISTANCE CIRCUIT CONTROLLED BY MECHANICAL RESONANCE OF TRANS- DUCER. Patent dated May 27, 1969. Disclaimer filed Apr. 4, 1969, by the inventor.

Hereby disclaims the terminal part of all claims of the patent subsequent to Oet.3,1983.

[O ficial Gazette January 13, 1.970.] 

